first paper; in other words, it contains from three to four per cent of iron protoxide. The lithiophilite, associated with the green chloritic mineral, has a light clove-brown color. It has a brilliant luster and is clear and transparent. The specific gravity is 3.482. An analysis* by Mr. S. L. Penfield, afforded the following results:

The ratio, P:R: R=636: 631: ·628, corresponds very closely with the formula previously accepted,

It will be observed that the amount of iron in this variety of the mineral is considerably greater than in that first described and alluded to above. This result is not surprising, and indeed was anticipated from the color of the specimen. Mr. Penfield, in the article referred to, has brought together the analyses of several varieties of triphylite and the two of lithiophilite, and thus shows the gradations between the two species. The one extreme is the Bodenmais triphylite with 36-21 p. c. FeO, and 8.96 p. c. MnO, and the other the original lithiophilite, with 4.02 p. c. FeO, and 40'86 p. c. MnO. The relation between these two minerals, is closely analogous to that existing between the iron and manganese carbonates, siderite (FeCO3), and rhodochrosite (MnCO). There is the same similarity in physical characters, the most pronounced difference being here as there in the color, so that the necessity of giving the two minerals of the triphylite group distinct names cannot be questioned.

EOSPHORITE.

The eosphorite we have spoken of as forming nodules imbedded in the massive green chloritic mineral. It occurs only massive, but shows the characteristic cleavage distinctly and is clear and lustrous. The color is a beautiful pink, sometimes quite deep. The specific gravity is 3.11. An analysis by Mr. Horace L. Wells gave the following results:

* This analysis has already been published by Mr. Penfield in an article on the composition of triphylite; this Journal, March, 1879.

The ratio of P2O5: A10,: RO: H2O is very nearly 1:1:2:4 or that given in our former paper, and upon which the formula was based, viz:

=

R,AIP,010, 4H,0 or AlP,O,+2H2(Mn, Fe)O2+2aq.

THE GREEN MINERAL.

The larger part of this deposit consisted, as already stated, of a soft green compact mineral, varying in tint from light grayish and yellowish-green to dark blackish-green. Luster dull to greasy. Hardness = 2.5. Specific gravity of the purest portions 2.85 to 2.89. This material was exceedingly impure, containing, imbedded in it, the feldspar and mica of the vein, also quartz, apatite, chabazite, as well as the phosphates, most conspicuously among these, the eosphorite. It was possible, however, to obtain small hand specimens showing the green mineral in a state of comparative purity. A series of ten thin sections was prepared from specimens which appeared most homogeneous, and these were carefully examined under the microscope. It was found from them, that the substance was, for the most part, fine granular and crypto-crystalline, but that numerous quartz grains and apatite needles were scattered through it. The crypto-crystalline ground-mass could not be resolved under the microscope and had every appearance of homogeneity, but it would be unsafe, considering the nature of the substance, to assert this positively. In any case the presence of distinct, though microscopic impurities, makes it quite hopeless to think of obtaining a definite chemical composition. A specimen as pure as we were able to obtain, has been analyzed by Mr. Horace L. Wells with the following result:

It is evident from the above, independent of the microscopic examination, that the substance analyzed is not a simple mineral. If we assume the 8.84 per cent of phosphoric acid to be combined with sufficient lime to form the mineral apatite, and deduct this amount and also the insoluble matter, we have a remainder of 75.19 per cent, which when calculated to the original amount gives the following composition:

It is scarcely admissible to attempt a formula for a substance which is so evidently a mixture, but we believe the results indicate that the green mineral is unquestionably a variety of chlorite. The analysis, excluding apatite and the insoluble residue, brings the composition very near that of delessite and prochlorite. Its physical characters, also, confirm its claim to be referred to the chlorite group.

The mineral gives water in the closed tube, and B. B. fuses to a black magnetic mass; with the fluxes it reacts for silica, iron and manganese. Soluble in hydrochloric acid with separation of silica, and an insoluble residue which was separated from the silica by solution of the latter in boiling carbonate of soda. The insoluble residue proved to be a silicate of alumina, possibly cymatolite which occurs at the locality in great abundance.

CHABAZITE.

This species occurs of a dark yellowish to reddish brown color, in irregular masses disseminated through quartz, and sometimes imbedded directly in the green chloritic mineral, and also in the massive manganesian carbonate occurring with the lithiophilite. A few small crystals, to inch over, were found in cavities. This singular mode of occurrence, in irreg ular spots and strings imbedded in other species, was so unlike the ordinary association of chabazite, that we could scarcely credit its being this species, although the pyrognostic characters, rhombohedral form (RR=96° 45'), density, hardness and other physical characters plainly indicated its specific relations. The analysis given below, however, renders its identification with chabazite complete; this analysis was made by Mr. Penfield on the purest material which could be obtained. It was found impossible to separate it entirely from the quartz.

The chabazite has a vitreous to sub-resinous luster. The hardness is 4.5 and the specific gravity is 2:16.

AM. JOUR. SCI.-THIRD SERIES, VOL. XVIII, No. 103.-JULY, 1879.

An analysis of a carefully selected specimen by S. L. Pen

field gave

=

It will be seen from what has been said in this and in our first paper, that rhodochrosite is a very common mineral in its association with the phosphates. In the first deposit it occurred sometimes in specimens of large size with the characteristic color and cleavage (RR 106° 49′), and again in granular aggregates interpenetrated with quartz, and often taking a greenish color from the dickinsonite. It also appears altered to a black, highly lustrous mineral, containing only the oxides of iron and manganese.

In the deposits which form the special subject of this paper, the rhodochrosite occurs first of a pink color implanted in the lithiophilite and hardly to be distinguished from it except by its cleavage; and again in large masses of a white or faintly pink color, granular texture, and made very impure from the admixture of quartz and apatite. This variety of the mineral occurs with the clove-brown lithiophilite and the green chloritic mineral, and contains in cavities crystals of quartz, apatite and chabazite. We add here an analysis by Mr. S. L. Penfield, of the first discovered rhodochrosite; specific gravity= 3.76.

The variation in color of the mineral implies that the composition varies widely, which would doubtless be shown, could analyses of different varieties be made. The interest connected with the subject is, however, small, although the large amount of iron present is worthy of note.

ART. VI.-Note on the Progress of Experiments for comparing a Wave-length with a Meter; by C. S. PEIRCE. Communicated by the Superintendent of the U. S. Coast and Geodetic. Survey.

To C. P. PATTERSON, Superintendent U. S. Coast and Geodetic Survey:

DEAR SIR-The following is the present state of the spectrum meter business. The deviation of a spectral line (Van der Willigen's No. 16) has had three complete measures using a certain gitter of 340 lines to the millimeter. The double deviation (the angle measured) was found to be

An error of 0.4" in this would occasion an error of one micron in the meter. These measures were previously communicated to you, but owing to an erroneous value of the coefficient of expansion of glass having been used (the value for iron having been inadvertently substituted) they did not seem to agree as well as they do. There were two other complete measures, but in regard to one of them there is a doubt about the thermometer used, and in regard to the other there is a doubt about the part of the line set on. This line seems on the whole to be a bad one for the purpose. Another line near it was therefore selected and another much finer gitter. deviations obtained were on the different days: 1879. May 8, 90° 03′ 51′′.7 May 15, 90° 03′ 50.35

May 9,
May 10,

51.75

May 21,

May 22,

The

51.75

52.0

Mean, 90° 03' 51'-45'

51.2

Notwithstanding the bad result of May 15, which is unaccountable, these measures are evidently good enough. One of these gitters has been compared with all the centimeters of a decimeter scale of centimeters. The other is still to be compared with all the even two centimeters of the same scale.

Mr. Chapman is now comparing this decimeter scale with all the decimeters of a meter scale of decimeters. As soon as that is done a meter will have been compared with a wave-length. But shortly after, this will be improved by comparing the other gitter and also a third upon which I propose to measure a deviation. It will remain, first, to find the coefficient of expansion of the glass meter. The apparatus is all ready for this and it will not take a fortnight. Second, the glass meter will have to be compared with a brass meter. This will be an operation of some difficulty but I think we shall complete it before long. Yours respectfully, C. S. PEIRCE, Assistant.